Many natural gases and process gases contain hydrogen sulfide, carbon dioxide and other impurities or contaminants. It is desirable to remove these impurities or contaminants from the natural gas before using the natural gas commercially. Hydrogen sulfide occurs naturally in natural gas and is referred to as “sour gas” when the hydrogen sulfide concentration is high. Hydrogen sulfide is also produced while refining petroleum and in other processes. Natural gas may contain as much as 90% hydrogen sulfide content. Hydrogen sulfide is toxic, flammable and cannot legally be released into the air.
Hydrogen may be found in nature in the elemental form, typically in trace amounts because hydrogen is reactive. Hydrogen is a desirable fuel because it is a clean burning fuel, i.e., its combustion produces only water. Unfortunately, hydrogen is often very expensive to produce and very difficult to store and transport. For example, a steel cylinder weighing about 50 pounds (23 kg) would typically contain only about 2½ ounces (71 g) by weight of hydrogen at a pressure of up to 3,000 psi (20,684 kPa). Because of the very high pressure and extreme flammability of hydrogen, these cylinders may be very dangerous.
Processes to remove hydrogen sulfide and carbon dioxide from gases are known. For example, hydrogen sulfide and carbon dioxide may be separated from gases by means of solvent extraction, adsorption, absorption or other means.
Processes to recover sulfur from hydrogen sulfide are also known. For example, in a conventional sulfur recovery process, known as the Claus Process, up to about one third of the hydrogen sulfide in a gas may be oxidized with air or oxygen into sulfur dioxide to react with the balance of the hydrogen sulfide and produce elemental sulfur and water. Part of this process is accomplished at temperatures above 850.degree. C. and part is accomplished in the presence of catalysts, such as activated alumina or titanium dioxide. The chemical reactions of the Claus Process are:2H.sub.2S+3O.sub.2.fwdarw.42SO.sub.2+2H.sub.2O4H.sub.2S+2SO.sub.2.fwdarw.3S2+4H.sub.2O
Frequently, the sulfur produced is of very low quality and often considered hazardous waste because of contamination principally caused by amine extractants commonly used entering the Claus Reactor with the hydrogen sulfide.
Another process is disclosed in U.S. Publication No. 2005/0191237. This publication discloses a process and apparatus for obtaining a hydrogen product and a sulfur product from a feed gas by separating the feed gas to obtain a purified hydrogen sulfide fraction of at least about 90% by volume hydrogen sulfide, dissociating the hydrogen sulfide in the hydrogen sulfide fraction to convert it into a purified hydrogen sulfide fraction of elemental hydrogen and sulfur, separating the dissociated purified hydrogen sulfide fraction to obtain a hydrogen rich fraction of elemental hydrogen, and obtaining the hydrogen product of elemental hydrogen. The dissociating is performed at a temperature of between 1500.degree. C. and 2000.degree. C.
U.S. Publication No. 2002/0023538 also discloses a process to remove hydrogen sulfide and other contaminants. This two-step process includes using a first adsorbent positioned in a fluidized bed operating at a temperature of about 20-60.degree. C. to remove at least a portion of the contaminants and using a second adsorbent positioned within another fluidized bed operating at a temperature of about 100-300.degree. C. to remove another portion of the contaminants from a gas. A conversion element, i.e., a nonthermal plasma corona reactor, is also disclosed for converting the contaminants to elemental sulfur and hydrogen at a temperature less than 400.degree. C.